2 Answers
2

If this performs well (fast enough for you) and returns not many rows (say, less than a 1000):

SELECT column FROM table
WHERE colA=123 ;

Then this will perform well, too, because it will sort only the (less than 1000) rows of the previous query:

SELECT column FROM table
WHERE colA=123
ORDER BY RAND()
LIMIT 10 ;

If you want to be dead sure that it will perform pretty well, even if the first query returns many thousands or million rows, you can use this, which will limit the sorting to maximum 1000 (or a number of your choice) rows: